1. Technical Field
The embodiments herein generally relate to magnetic sensing, and, more particularly, to locating magnetic objects.
2. Description of the Related Art
A system and method for tracking magnetic objects is described in U.S. Pat. No. 6,675,123 (hereinafter referred to as “the '123 patent”), the complete disclosure of which, in its entirety, is herein incorporated by reference. As the '123 patent describes, all types of land vehicles, ships, and aircraft have structural and power systems capable of generating substantial magnetic signatures. Even small objects may exhibit sufficient magnetization to be observed from a distance. These applications include covert handgun detection to protect buildings and their occupants; pinpointing unexploded ordnance at converted military bases; and locating the position and depth of underground pipes prior to construction activities. The ability to track magnetic objects is also crucially important in other areas, such as medicine. For example, controlling the orientation, forces, and/or motion of internally implanted devices.
A variety of magnetic sensor data processing algorithms, methods, systems and devices thereof capable of localizing, quantifying, and classifying objects based on their magnetic fields and magnetic signatures have been developed. Some conventional techniques detect, locate, and classify magnetic objects based on a large set of measurements distributed over space and/or time. Some conventional techniques involve using measurements of an object's magnetic dipole moment, or are based on electromagnetic anomaly detection technology, which senses an electromagnetic anomaly and pinpoints it as close to real time. Such a technique can measure how close a target is located to a sensor head, while locating the target or magnetic object in three dimensions and thereafter evaluating its orientation.
One of the problems associated with such conventional techniques for tracking magnetic objects is that they are generally based on the utilization of three components of a detected magnetic field. Typically, if measurements of the vector magnetic-field are made, great care must be taken to minimize rotational vibrations. However, because the earth's magnetic field is so large (i.e. on an order 50,000 nT), it is generally difficult to differentiate rotational vibrations from signals from an object.
Programs and methodologies based on such techniques typically require the inversion of a matrix and additionally require a relatively great deal of processing time. Such programs and methodologies also usually require obtaining measurements from several sensors simultaneously. In order to perform several measurements on nearby weak sources and to avoid rotational vibrations, the sensors should be placed close to one another on a rigid frame. If the sensors are configured in this manner, the difference between the signals from strong distant sources is generally small. Additionally, obtaining accurate measurements of these small differences requires expensive sensors and the use of gradiometer algorithms. Unfortunately, such techniques are generally time consuming and also inefficient. While the '123 patent provides a valuable technique for overcoming the problems of the conventional techniques for finding the track of magnetic objects, there remains a need for finding the position of the target as a function of time on the track of magnetic objects.